An all-solid-state battery (ASSB) can provide the energy density and safety requirements for electric vehicles in the future. For an ASSB to be functional, there must be sufficient contact formed between the solid electrolyte and the solid electrode materials. This is typically achieved by sintering, a process which involves heating a compacted monolithic body of powder for a period of time during which the body densities and the internal pores are greatly reduced or eliminated. Many solid electrolyte and solid electrode materials react under normal sintering conditions, yielding a different chemical composition than was initially chosen based on capacity and efficiency considerations. The reacted phases formed after sintering result in a densified body, but a non-functional ASSB.
A lithium titanate (Li4Ti5O12) (LTO) based all-solid-state battery offers significant improvements in safety, energy density, and thermal stability over conventional LTO-based Li-ion batteries. During sintering, LTO reacts with the solid electrolyte and forms inactive phases of lithium, titanium, and oxygen. LTO is more stable during sintering with lithium lanthanum titanium oxide (LLTO) (Li3xLa2/3-xTiO3) as the solid electrolyte, however, LTO and LLTO still react at the elevated temperatures required for sintering. For example, sintering of 50:50 by weight mixture of LTO and LLTO at 1000° C. for 10 hours will result in the formation of new phases of lithium, titanium, and oxygen, comprising 58% by weight of the composite, and a reduction in the amount of original active LTO and LLTO phases to just 3% and 38% by weight, respectively.